We are more confident because we know ourselves better. We know what we don't want. We know what will hurt and what will strengthen. We know what will make us happy or frustrate us.
Sure we know all that... but our hearts are still young fools. We still love whether or not it's good for us. We just know how to tell ourselves when it's enough, when it's time to say "no" and move on. We don't want to drag it out anymore.
I think it's easy to fall in love when you feel a connection to someone. It feels good even if they don't reciprocate because it gives you hope that you will find someone else like them who will love you back. There's a little struggle to let them go... but you're used to that by now. This isn't your first dance.